devfreq: memlat: Add suspend/resume for mem_latency

Add suspend/resume support for the mem_latency governor. Uses hwmon driver-
defined suspend/resume calls in addition to monitor start/stop calls within
the devfreq framework.

Change-Id: I900b322a05cd0312f082d70640e21851879cb18c
Signed-off-by: Jonathan Avila <avilaj@codeaurora.org>
[avajid@codeaurora.org: made minor styling changes]
Signed-off-by: Amir Vajid <avajid@codeaurora.org>